How does Wolfram's Image Identification Project work?
The ImageIdentify project uses the highly automated "superfunctions" and as part of Wolfram Language API integration. It relies on a complex collection of meta-algorithms and built-in 'knowledge'. It has a built-in classifier trained from a large dataset using Wolfram Data Framework (WDF). However the main classifier is based on the deep neural networks.

Source: How the Wolfram Language Image Identification Project Works

The algorithm isn't perfect and misidentification are more likely to be caused by 'irrelevant objects repeatedly being in training images for a particular type of object'.

You can read more at Wolfram Language Artificial Intelligence: The Image Identification Project.